The broad, long-term objective of this study is the development of an invertebrate model system allowing the study of excitability of a heart- like muscle by the full array of pharmacological, electrophysiological, molecular, and genetic techniques, with the emphasis on molecular genetics. This model will be used to identify molecules important in excitability, which may help in understanding diseases (e.g., arrhythmias) that can result from defects in cardiac excitability, and in understanding and developing pharmacological agents to treat these diseases. The model is the pharyngeal muscle of the nematode Caenorhabditis elegans. a) Identification of genes that affect pharyngeal muscle excitability. Mutants will be isolated that show abnormalities in pharyngeal muscle motions; b) Genetic analysis of eat-5, which affects coupling of pharyngeal muscles; c) Genetic analysis of eat-6, probably necessary for normal pharyngeal muscle repolarization. Classical genetic methods will be used to determine how pharyngeal muscle behavior is affected by complete loss of eat-5 or eat-6 function, when the genes act, and how they interact; d) Molecular cloning and characterization of eat-5; e) Molecular cloning and characterization of eat-6. RFLP and deletion mapping will be used to correlate the genetic and physical maps of the C elegans genome in the vicinity of eat-5 and eat-6. The genes will be identified by their ability to rescue the phenotype of mutant worms. cDNAs will be isolated and sequenced, and f) Pharmacological characterization of the function of isolated pharynxes. Pharynxes will be dissected out of worms and their function studied in vitro.